As is well known, sufficient portions of the VHF and UHF spectra have been allocated to accommodate twelve VHF and seventy UHF channels for broadcasting and receiving television signals. Conventional television receivers almost invariably employed separate, usually mechanical, tuners with individual tuning knobs for the selection of either VHF or UHF channels. More recently, electronic tuners and frequency synthesis techniques have given rise to dramatic improvements in television channel selection systems. These improvements have generally been directed to reducing the size and cost while enhancing the performance and reliability of the receiver's channel-selection mechanism.
A particular approach allows both VHF and UHF channels to be selected by a single tuning knob. This approach is especially appropriate for use in conjunction with channel-selecting devices that include a digitally-controlled tuning synthesizer, such as the commercially available NITRON NC6405. For the purposes of understanding this invention, it is sufficient to consider the synthesizer's output frequency as being determined by the digital count present at its input. One-knob tuning can be effectuated by coupling the tuning knob to an electronically encoded shaft according to any of a number of known shaft-encoding techniques. As the viewer rotates the knob output pulses are developed and coupled to the synthesizer in a fashion that increments or decrements the count at its input, thereby providing access to all twelve VHF and all seventy UHF channels.
Despite the apparent advantages of such a channel-selection system, it might have been expected that in a situation where changing channels necessitates bypassing a large number of channels, as when changing from a low VHF to a high UHF channel, an inordinant amount of tuning knob rotation is required. The subject invention detects such a situation and effects more rapid channel changing in response.